The present invention relates generally to a current controlled motor amplifier system.
The conventional approach to transconductance or current controlled motor amplifier design includes current sensing, scaling, error amplification, compensation, and motor drive. One example of such an amplifier is shown in FIG. 1 in which T1, T2, T3, and T4 are solid-state switches (usually transistors), M is the electric motor (or one phase of the motor in the case of a multiphase motor), and I is the current in the motor. A reverse biased diode is connected to each switch. The upper and lower terminals of the H bridge are connected to maximum potentials.
The conventional approach is used specifically in areas where significant motor rotational velocities result in high motor back-EMF (electromagnetic force). By sensing the motor current, and developing a current signal proportional to the motor current, the instantaneous motor current can be compared with the commanded motor current. Any difference between the commanded and measured motor current is amplified as an error signal that is the command signal to the motor drive bridge. If the measured current is smaller than the commanded current, then the error signal will command a compensatory increase in motor current. In this way, the output current, and hence an output torque of the motor is proportional to the input command to the amplifier.
The conventional approach is usually well suited to driving motors over a wide range of loads and rotational velocities. A problem with the conventional approach is that it addresses a larger situation than that of the typical force-feedback application, such as wheel or joystick amplifiers in gaming applications, which tend to operate close to stall, or at comparatively low rotational velocities. The breadth of coverage in the conventional approach adds unnecessary complexity to the motor amplifier design for force-feedback applications.
Accordingly, what is needed is an approach to current controlled motor amplifier design that is less complex and more suitable for high fidelity force feedback applications.
Aspects of a current controlled motor amplifier system are provided. These aspects include a current source motor amplifier comprising current source means on each leg of a top half of the H bridge configuration and switching means on each leg of a bottom half of the H bridge configuration. A motor is coupled to the current source motor amplifier at a center portion of the H bridge configuration. Control circuitry is coupled to the current source motor amplifier for controlling the switching on of the current source motor amplifier for a predetermined time to operate the top half of the H bridge configuration essentially as a linear constant current source and the bottom half of the H bridge configuration in switching mode.
Through the present invention, significant current loop delays associated with conventional approaches are avoided. Further, the present invention provides a less complex and less costly solution that includes overvoltage protection and is more suitable for high fidelity force feedback when changing direction of motor rotation. The present invention also provides for a simple means of motor back EMF compensation. These and other advantages will become readily apparent from the following detailed description and accompanying drawings.